This invention generally relates to techniques for forming electrostatic discharge (ESD) protection for a computer disk, commonly called a hard disk drive (HDD), throughout its assembly process. More particularly, the present invention provides robust methods and dry processes for preventing electrostatic discharge and circuit noise induced by circuit handling during HDD assembly. Merely by way of example, the present invention is implemented using such methods and processes with a dissipative carbon base thin film coating on a flexible circuit to drain the potential electrostatic charge during circuit assembly and interconnect processes, yet it would be recognized that the invention has a much broader range of applicability on any electronic apparatus that is susceptible to electrostatic damage and static noise.
Nowadays, a HDD uses a magnetoresistive thin film element (MR Head) to perform data read/write operation. The MR Head is bonded on a slider and then connected to a flex circuit for data transmission. A suspension provides a platform for this architecture that forms a head gimbal assembly (HGA). Production yield of this assembly is critical for overall HDD cost margin. Yet, this thin film head element is susceptible to low voltage ESD damage, and the signal is susceptible to static noise distortion.
The common protection tactics are to coat dissipative polymer film on circuits to drain out potential charges and/or ground the slider with conductive material to minimize noise. However, these tactics have disadvantages. For example, due to the natural properties of the polymer film, the resistance and thickness uniformity of the polymer film are hard to control. Furthermore, the polymer film suffers from environmental attack (e.g., temperature, humidity, etc.) and requires curing time. With respect to techniques of grounding the slider, they have the disadvantage of high cost due to forming the grounding feature on circuit by sputtering and/or deep-hole plating followed by nickel (Ni) and gold (Au) plating. Other techniques using solder or conductive epoxy have high ground resistance due to the presence of oxide on the ground plane surface.
The HDD industry has long sought a clean, low cost, and robust coating to perform the ESD protection and noise reduction. Thus, there is a great need for a robust and low cost solution.